The present invention relates to an apparatus for detecting machining states of a workpiece in a machine tool during a machining process.
Based on prior art techniques for detecting machining states in a machine tool during a machining process, variables for detection are a machining force, vibrations, sounds, heat and machining power or machining dimensions (residual stock removal amount).
Case of machining force
The machining force is detected by use of (1a) a distortion gauge or a piezoelectric element which are mounted on a work holder of a milling machine or a tool holder on a lathe and (1b) a distortion gauge mounted on a work holding for external cylindrical grinder center or on the basis of (1c) variations in pocket pressure of a hydrostatic fluid bearing which supports a tool (workpiece) spindle.
Case of Vibrations and Sounds
The vibrations and sounds are detected by use of (2a) an AE sensor or a vibration sensor which are provided on the work holder, the tool holder, work holding center or a work holding shoe and (2b) one AE sensor or the vibration sensor which are attached to the tool (workpiece) spindle supported by rolling bearing.
Case of Heat
(3) The heat is detected by heat detection sensors embedded in the workpiece or the tool.
Case of Machining Power
The detection of the machining power involves a detection of rotary driving power of the tool (workpiece) spindle.
Case of Machining Dimensions (Residual Stock Removal Amount
The machining dimensions are detected on the basis of a difference between a feed amount and removed amount during the machining process.
The following are defects inherent in the above-mentioned techniques for detecting the machining states.
Case of Machining Force.
The detection of machining force is (1a) limited to a case where the workpiece is movable within a given range as well as restricting a support rigidity thereof, (1b) limits the workpiece which must be held between conical centers, and (1c) is limited in slow.
Case of Vibrations and Sounds
The detections of vibrations and sounds are only effective for abnormal state detection and not effective for normal state detection, and (2b) sensing through the bearing, a vibration amplitude is diminished also S/N ratio is lowered because of detecting rolling vibrations of the hearing.
Case of Heat
The detection of heat is (3) not practical at production shop and has slow respondency as well.
Case of Machining Power
The detection of machining power is (4), in addition to a slow respondency detection is, limited to the tangential force to the workpiece surface and this method is insufficient for a grinding process wherein the force variations in a normal to the surface are large.
Case of Machining Dimensions (Residual Stock Removal Amount);
The detection of machining dimensions is slow of respondency because of being detected after effecting the machining process.
In any case, these detecting methods have slow respondency or are not accurate enough. Besides, the above-mentioned methods are simple condition-detecting methods have but not yet reached a level to analyze various states by highly accurate detection and to output a signal capable of effecting the corresponding control over the machine tool.